Today's industrial production leaves many types of waste materials, including chemical waste materials, which for environmental reasons have to be disposed of, i.e. converted into an environmentally acceptable form, by incineration, for instance in a rotary furnace. At incineration in a rotary furnace, the calorific value of the problematic waste can be utilized. If, after incineration, the waste type leaves ashes or cinders, the disposal of which may still cause environmental problems, it may be advantageous to incinerate the waste in a cement kiln, confer as an example WO publication No. nr. 94/09319.
Some of the problematic waste materials are difficult to handle, as they are in a solid or pastose form. Such materials are difficult to feed into a combustion furnace under stable conditions, so that a fairly constant and sufficiently high combustion temperature can be maintained. In order to ensure a uniform and adjustable feeding of the waste material, it is advantageous, if the material is easily converted into a pumpable material.
EP patent No. 73.787 discloses a method of processing a nonpumpable, solid or viscous problematic waste material, such as discarded paints, paint sludge, greasy wastes, distillation residues, which may contain oil sludge, organic compounds and the like, wherein the waste is subjected to a mechanical reduction in size and simultaneously or subsequently dispersed with water to saturation at mechanical mixing, whereby a pumpable dispersion is obtained, which can be used as a fuel. However, experience has shown that this method cannot be used for all types of waste.
Another problem when incinerating chemical wastes is that certain types of waste may be highly active, whereby explosions may occur, if high concentrations of said wastes are fed into a combustion furnace.
Certain types of particularly active wastes may cause problems in form of heavy exothermic reactions creating explosions merely by being vigorously ground.
WO publication No. 91/01185 discloses a method for utilizing residues and waste waters from paint shops and lacquer processing installations, in particular lacquer and paint sludges, and colorant waste from the automobile industry, i.a. by utilizing the calorific value of the organic compounds contained therein. By this method, the varying and possibly mechanically drained residues are collected separately in closed transport containers from the different places, in which the waste occurs, and transported to a central processing and utilization plant. In this plant, the residues, containing volatile organic compounds and/or water under the selected process conditions, are dried and ground in a heated, continuously driven contact drier at 120.degree. C. to 250.degree. C. under a slight vacuum and while being kneaded and mixed. For some types of waste, such a drying process at an increased temperature results in caking or hardening, which makes it impossible to convert the waste material into a pumpable form, which may be injected through a nozzle into a combustion furnace at a later stage. Moreover, there is a risk of explosions when drying at such high temperatures.
DE patent No. 3.900.482 discloses a method for the disposal of lacquer and paint sludges and colorant wastes, in particular from the automobile industry, wherein the wastes, subsequent to any thorough separation of volatile solvents and possibly while being cooled, are ground and mixed with at least the same quantity of coal dust and possibly with alkaline additives, preferably quicklime and/or limestone powder, whereafter it may be burnt. This method cannot either be used for the most difficult types of chemical wastes, in particular such wastes leaving a solid mass which is difficult to grind or cannot be ground at all, subsequent to removal of any solvents.
EP patent application No. 288.913 discloses a method for disposal of acid-soluble materials, wherein the materials initially are dissolved in a strong acid, whereafter the solution is fed into an incineration plant. However, this method is generally not usable with varying types of chemical wastes.
FR published specification No. 2.702,488 discloses a method for the preparation of fuel especially from industrial waste, in which portions of a reasonably homogeneous composition are prepared, a large number of chemical and physical analyses are performed on each portion, the amounts of material from the available, analyzed portions which can be combined to obtain pastose or viscous fuel are determined, solid wastes are ground to a particle size of between 10 or 25 mm and amounts thereof are added to the other constituents and admixed to a fuel material having a viscosity of preferably 150 poise, i.e. 15 Pa.multidot.s. Some of the analyses performed are chemical analyses of different harmful substance, such as chlorine, sulphur and heavy metals to ensure that the end fuel is within the the maximum limit values set by the authorities. The intercompatibility of the different solid and liquid waste portions is thus not tested, whereby such a possible compatibility cannot be utilized optimally to dissolve or swell the solid or viscous waste constituents to obtain an advantageous reduction in the viscosity. According to the French patent a piston pump, such as a concrete pump, is required for pumping of the prepared high-viscose fuel, as a high pump pressure is required, e.g. 150 bar (15 MPa). The material is thus not so liquid that it can be pumped at a considerably lower pressure, which is used in a single-stage centrifugal pump having a pump pressure of typically 3-4 bar (0.3-0.4 MPa).